Please wait a minute...
Just Accepted | Current Issue | Archive | Featured Articles | Special Issue | Most Read | Most Downloaded | Most Cited
Acta Metall Sin  2018, Vol. 54 Issue (4): 547-556    DOI: 10.11900/0412.1961.2017.00357
Orginal Article Current Issue | Archive | Adv Search |
Plasma-MIG Hybrid Welding Hot Cracking Susceptibility of 7075 Aluminum Alloy Based on Optimum of Weld Penetration
Yingkai SHAO, Yuxi WANG, Zhibin YANG(), Chunyuan SHI
School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China
Cite this article: 

Yingkai SHAO, Yuxi WANG, Zhibin YANG, Chunyuan SHI. Plasma-MIG Hybrid Welding Hot Cracking Susceptibility of 7075 Aluminum Alloy Based on Optimum of Weld Penetration. Acta Metall Sin, 2018, 54(4): 547-556.

Download:  HTML  PDF(10406KB) 
Export:  BibTeX | EndNote (RIS)      
Abstract  

The 7075 aluminum alloys have major applications in commercial, transportation industry and military air carriers, owing to their associated light weight, high strength, good machinability, high fracture toughness and low fatigue crack growth. Several welding techniques, such as metal inert gas (MIG) welding, tungsten inert gas (TIG) welding, laser welding and friction stir welding (FSW), have been applied to weld the 7075 aluminum alloys. However, their applications are limited because of the lower weld strength, slower welding speed and other significant limitations of them. Among the different welding techniques, plasma-MIG hybrid welding is a new fabrication technique with many advantages such as stable welding process, no weld spatter, the decreased pores, small grain size and high joint quality. Up to now, the study mainly focuses on coaxial plasma-MIG hybrid welding, and it is rare in dealing with the hot cracking susceptibility of 7000 series aluminum alloys welded by paraxial plasma-MIG hybrid welding. In this work, the paraxial plasma-MIG hybrid welding system was used to weld 7075-T6 aluminum alloy plates. The quantitative relationship between plasma-MIG hybrid welding parameters of 7075 aluminum alloy and weld penetration was established by linear regression orthogonal test. Hot ductility tests were studied by using the thermal simulated test to determine the brittleness temperature range of the alloy. Welding hot cracking susceptibility tests were conducted by using the fish bone method, and the type and cause of the hot cracking were analyzed by SEM, EDS and OM. The results indicated that the brittleness temperature range of 7075 aluminum alloy was 470~620 ℃. When the heat inputs of plasma-MIG hybrid welding were 2.52, 2.95 and 3.42 kJ/cm respectively, the welding hot cracking susceptibility decreased and then increased with the heat input increasing. The type of cracking in partially melted zone of base metal was liquation cracking, and that of weld zone was solidification cracking. When the heat input was 2.95 kJ/cm, the welding hot cracking sensitivity was the least, and the welding cracking was solidification cracking. Compared to MIG welding joints, the hot cracking susceptibility of plasma-MIG hybrid welding joints decreased by 47% under the same conditions.
Key words:  7075 aluminum alloy      plasma-MIG hybrid welding      weld penetration      welding hot cracking susceptibility     
Received:  29 August 2017     
ZTFLH:  TG406  
Fund: Supported by General Project of Education Department of Liaoning Province (No.JDL2016009)
Service
E-mail this article
Add to citation manager
E-mail Alert
RSS
（）
Articles by authors
Yingkai SHAO
Yuxi WANG
Zhibin YANG
Chunyuan SHI

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2017.00357     OR     https://www.ams.org.cn/EN/Y2018/V54/I4/547

Material Si Fe Cu Mg Zn Ti Pb Cr Mn Al
7075-T6 0.09 0.29 1.45 2.23 5.34 0.05 0.03 - - Bal.
ER5183 0.3 0.1 0.1 4.5 - 0.1 - 0.1 0.8 Bal.
Table 1  Chemical compositions of 7075-T6 aluminum alloy and ER5183 (mass fraction / %)
Material Yield strength / MPa Tensile strength / MPa Elongation / %
7075-T6 ≥435 ≥505 ≥8
ER5183 ≥125 ≥275 ≥17
Table 2  Mechanical properties of 7075-T6 aluminum alloy and ER5183
Fig.1  Schematic of samples for hot ductility tests (unit: mm)
Fig.2  Schematic of samples for fish-bone welding hot cracking tests (unit: mm)
Level zj IP (x1) IMIG (x2) v (x3) Q (x4)
Lower -1 80 120 90 5
Zero 0 100 150 100 6
Upper 1 120 180 110 7
Range Δj 20 30 10 1
Table 3  Levels of nature factors and its codings
Fig.3  Partial weld formation of orthogonal test schemes

(a) No.1 (b) No.2 (c) No.3

No. z1 z2 z3 z4 IP (x1) IMIG (x2) v (x3) Q (x4) y Forming condition
1 1 1 1 1 120 180 110 7 4.00 Over penetration
2 1 1 -1 -1 120 180 90 5 4.00 Well-formed
3 1 -1 1 -1 120 120 110 5 2.46 Lack of penetration
4 l -1 -1 1 120 120 90 7 4.00 Over penetration
5 -1 1 1 -1 80 180 110 5 3.04 Lack of penetration
6 -1 1 -1 1 80 180 90 7 4.00 Well-formed
7 -1 -1 l 1 80 120 110 7 1.68 Lack of penetration
8 -1 -1 -1 -1 80 120 90 5 2.14 Lack of penetration
9 0 0 0 0 100 150 100 6 3.30 Lack of penetration
10 0 0 0 0 100 150 100 6 3.51 Lack of penetration
11 0 0 0 0 100 150 100 6 3.06 Lack of penetration
Table 4  Orthogonal test scheme and its results
Source of variance SS Df MS F Significance
z1 1.6200 1 1.6200 15.55 * *
z2 2.8322 1 2.8322 27.18 * *
z3 1.0952 1 1.0952 10.51 *
z4 0.5202 1 0.5202 4.99 *
Regression 6.0676 4 1.5169 14.56 * *
Residual 0.6253 6 0.1042
Sum 6.6929 n-1=10
Table 5  Analyses of significance of the linear multivariate regress equation
Fig.4  Weld formation at optimized parameters
Fig.5  Rm-T curve during heating process (Rm—tensile strength, T—temperature)
Fig.6  SEM image of fracture surface of sample at zero strength temperature
Fig.7  Z-T curve during cooling process (Z—reduction of area)
Fig.8  SEM image of fracture surface of sample at zero ductility temperature
Fig.9  Macrostructures of samples after hot cracking susceptibility tests

(a) 2.52 kJ/cm (b) 2.95 kJ/cm (c) 3.42 kJ/cm (d) MIG-2.95 kJ/cm

Welding process Heat input / (kJcm-1) Cracking sensitivity / % Mean cracking sensitivity / %
Plasma
-MIG







 2.52 72.92 86.39
92.50
93.75
2.95 39.58 45.14
50.00
45.83
3.42 84.58 85.14
86.25
84.58
MIG 2.95 88.56 88.86
90.15
87.86
Table 6  Results of welding hot cracking susceptibility tests
Fig.10  Microstructures of WZ (a, c, e) and PMZ (b, d, f) of hot cracking at the heat inputs of 2.52 kJ/cm (a, b), 2.95 kJ/cm (c, d) and 3.42 kJ/cm (e, f) (WZ—weld zone, FZ—fusion zone, PMZ—partially melted zone)
Fig.11  Microstructures of fracture surface of samples at the heat input of 2.52 kJ/cm (a), 2.95 kJ/cm (b) and 3.42 kJ/cm (c)
Fig.12  SEM image (a) and EDS element maps of Al (b), Mg (c), Zn (d) of the area around the crack in PMZ of base metal at 2.52 kJ/cm
Position Al Cu Mg Zn
1 93.22 1.73 2.51 2.54
2 93.05 2.30 2.25 2.40
3 92.25 2.11 2.89 2.75
Mean 92.84 2.05 2.55 2.56
Table 7  EDS analyses of grain boundary of PMZ in Fig.12a (atomic fraction / %)
[1] Chen C Q.Development of ultrahigh-strength aluminum alloys[J]. Chin. J. Nonferrous Met., 2002, 12(S1): 22(陈昌麒. 超高强铝合金的发展[J]. 中国有色金属学报, 2002, 12(S1): 22)
[2] Zhou J.Microstructures evolution and processing simulation of 7075 aluminum alloy in forging process [D]. Shenyang: Northeastern University, 2003(周建. 7075铝合金在锻造过程中显微组织的演变和工艺模拟 [D]. 沈阳: 东北大学, 2003)
[3] Azizi A, Alimardan H.Effect of welding temperature and duration on properties of 7075 Al to AZ31B Mg diffusion bonded joint[J]. Trans. Nonferrous Met. Soc. China, 2016, 26: 85
[4] Holzer M, Hofmann K, Mann V, et al.Change of hot cracking susceptibility in welding of high strength aluminum alloy AA 7075[J]. Physics Procedia, 2016, 83: 463
[5] Liu C J, Sun J, Zhang W, et al.Effect of microstructure and property of welded joint of by double-pulsed MIG welding process with different wires[J]. Hot Working Technol., 2016, 45(19): 203(刘长军, 孙佳, 张威等. 不同焊丝对7075铝合金双脉冲MIG焊缝组织与性能的影响[J]. 热加工工艺, 2016, 45(19): 203)
[6] Tian S.CO2 laser welding of 7075 high strength aluminum alloy with filler wire [D]. Beijing: Beijing University of Technology, 2005(田盛. 7075高强铝合金CO2激光填丝焊接的研究 [D]. 北京: 北京工业大学, 2005)
[7] Rao T S, Reddy G M, Rao S R K. Microstructure and mechanical properties of friction stir welded AA7075-T651 aluminum alloy thick plates[J]. Trans. Nonferrous Met. Soc. China, 2015, 25: 1770.
[8] Kumar S R, Rao V S, Pranesh R V.Effect of welding parameters on macro and microstructure of friction stir welded dissimilar butt joints between AA7075-T651 and AA6061-T651 alloys[J]. Procedia Mater. Sci., 2014, 5: 1726
[9] Sivaraj P, Kanagarajan D, Balasubramanian V.Fatigue crack growth behaviour of friction stir welded AA 7075-T651 aluminium alloy joints[J]. Trans. Nonferrous Met. Soc. China, 2014, 24: 2459
[10] Schevers A A.Plasma-MIG welding of aluminum[J]. Weld. Met. Fabr., 1976, 44: 17
[11] Lee H K, Park S H, Kang C Y.Effect of plasma current on surface defects of plasma-MIG welding in cryogenic aluminum alloys[J]. J. Mater. Process. Technol., 2015, 223: 203
[12] Zhou D Z, Sun J, Huang Z P.Single power source plasma-MIG welding process[J]. Trans. Chin. Weld. Inst., 1990, 11(3): 1(周大中, 孙军, 黄子平. 单电源等离子-MIG焊方法[J]. 焊接学报, 1990, 11(3): 1)
[13] Bai Y, Gao H M, Qiu L.Droplet transition for plasma-MIG welding on aluminum alloys[J]. Trans. Nonferrous Met. Soc. China, 2010, 20: 2234
[14] Que F H, Wang Z M.Research progress in the plasma-MIG welding[J]. Electr. Weld. Mach., 2013, 43(3): 28(阙福恒, 王振民. 等离子-MIG焊的研究发展[J]. 电焊机, 2013, 43(3): 28)
[15] Lee H K, Chun K S, Park S H, et al.Control of surface defects on plasma-MIG hybrid welds in cryogenic aluminum alloys[J]. Int. J. Nav. Arch. Ocean Eng., 2015, 7: 770
[16] Liu Z.Research on plasma-MIG hybrid welding process of AZ31B magnesium alloy profiles [D]. Chengdu: Southwest Jiaotong University, 2013(刘正. AZ31B镁合金型材等离子-MIG复合焊工艺研究 [D]. 成都: 西南交通大学, 2013)
[17] Yang T.Research on arc coupling mechanism and welding technology of plasma-MIG hybrid arc welding process for 2219 aluminum alloy [D]. Harbin: Harbin Institute of Technology, 2013(杨涛. Plasma-MIG电弧耦合机制及2219铝合金焊接工艺研究 [D]. 哈尔滨: 哈尔滨工业大学, 2013)
[18] de Resende A A, Ferraresi V A, Scotti A, et al. Influence of welding current in plasma-MIG weld process on the bead weld geometry and wire fusion rate[J]. Weld. Int., 2011, 25: 910
[19] Liu X T, Cui J Z.Progress in research on ultra high strength Al-Zn-Mg-Cu alloy[J]. Mater. Rev., 2005, 19(3): 47(刘晓涛, 崔建忠. Al-Zn-Mg-Cu系超高强铝合金的研究进展[J]. 材料导报, 2005, 19(03): 47)
[20] Niu J T.Physical Simulation in Materials and Hot-Working [M]. Beijing: National Defense Industry Press, 1999: 1(牛济泰. 材料和热加工领域的物理模拟技术 [M]. 北京: 国防工业出版社, 1999: 1)
[21] Reddy G M, Mukhopadhyay A K, Rao A S.Influence of scandium on weldability of 7010 aluminium alloy[J]. Sci. Technol. Weld. Joining, 2015, 10: 432
[22] Zhang Y, Chen G Y, Chen B H, et al.Experimental study of hot cracking at circular welding joints of 42CrMo steel[J]. Opt. Laser Technol., 2017, 97: 327
[23] Kolarik L, Kovanda K, Kola?íková M, et al.Weldability test of precipitation hardenable aluminium alloy EN AW6082-T6[J]. Mm Sci. J., 2011, 6: 242.
[24] Wei B.Research on hybrid plasma-MIG welding progress of aluminum alloys [D]. Chengdu: Southwest Jiaotong University, 2014(魏波. 铝合金等离子-MIG复合焊工艺研究 [D]. 成都: 西南交通大学, 2014)
[25] Prokhorov N N.Problems of the strength of metals in the process of solidification during welding[J]. Weld. Prod., 1956, 6: 5
[26] Doumont M, Lefebvre W, Doisneau-Cottignies B, et al.Characterisation of the composition and volume fraction of η' and η precipitates in an Al-Zn-Mg alloy by a combination of atom probe, small-angle X-ray scattering and transmission electron microscopy[J]. Acta Mater., 2005, 53: 2881
[27] Wagner J A, Shenoy R N.The effect of copper, chromium, and zirconium on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloys[J]. Metall. Trans., 1991, 22A: 2809
[28] Wang H B, Huang J F, Yang B, et al.Current status and future directions of ultrahigh strength Al-Zn-Mg-Cu aluminum alloys[J]. Mater. Rev., 2003, 17(9): 1(王洪斌, 黄进峰, 杨滨等. Al-Zn-Mg-Cu系超高强度铝合金的研究现状与发展趋势[J]. 材料导报, 2003, 17(9): 1)
[29] Peng Y, Xu L H, Tian Z L, et al.Effect of heat input on microstructure and mechanical properties of the high strength aluminum alloy welds[J]. Trans. China Weld. Inst., 2008, 29(2): 17(彭云, 许良红, 田志凌等. 焊接热输入对高强铝合金的接头组织和性能的影响[J]. 焊接学报, 2008, 29(2): 17)
[30] Zhou G T, Liu X S, Li X H, et al.Transverse compressive pre-stress method for controlling welding hot cracking of aluminum thin-plate[J]. Chin. J. Nonferrous Met., 2009, 19: 613(周广涛, 刘雪松, 李晓红等. 预置横向挤压载荷法防止铝合金薄板焊接热裂纹[J]. 中国有色金属学报, 2009, 19: 613)
[31] Safari A R, Forouzan M R, Shamanian M.Hot cracking in stainless steel 310s, numerical study and experimental verification[J]. Comput. Mater. Sci., 2012, 63: 182
[32] Dong W K.Research on the grain boundary liquation in the heat affected zone of 7N01 aluminum alloy welded joints [D]. Shenyang: Northeastern University, 2013(董未科. 7N01铝合金焊接接头热影响区晶界液化的研究 [D]. 沈阳: 东北大学, 2013)
[33] Huang C, Kou S.Liquation cracking in full-penetration Al-Cu welds[J]. Weld. J., 2004, 83: 111S
[1] GAO Chuan, DENG Yunlai, WANG Fengquan, GUO Xiaobin. Effect of Creep Aging on Mechanical Properties of Under-Aged 7075 Aluminum Alloy[J]. 金属学报, 2022, 58(6): 746-759.
[2] SU Ruiming, QU Yingdong, LI Rongde. PRE-AGING OF RETROGRESSION AND RE-AGING OF SPRAY FORMED 7075 ALLOY[J]. 金属学报, 2014, 50(7): 863-870.
[3] KANG Ju LUAN Guohong FU Ruidong. MICROSTRUCTURES AND MECHANICAL PROPERTIES OF BANDED TEXTURES OF FRICTION STIR WELDED 7075-T6 ALUMINUM ALLOY[J]. 金属学报, 2011, 47(2): 224-230.
[4] LIU Xiaomin; QIAO Lijie; CHU Wuyang(Department of Materials Physics; University of Science and Technology Beijing; Beijing 100083)Coerespondent: LIU Xiaomin; Tel: (010)62332906. EMBRITTLEMENT BEHAVIOR OF 7075 ALUMINUM ALLOY IN LIQUID METAL Ga[J]. 金属学报, 1998, 34(6): 615-620.
[5] LIU Xiaomin; SU Yanjing; HUANG Yizhong; CHU Wuyang(Department of Materials Physics; University of Science and Technology Beijing; Beijing 100083)Correspondent: LIU Xiaomin; Tel: (010)62332906; Fax:(010)62327283;E-mail: ljqiao@public.bta.net.cn). IN SITU TEM OBSERVATION OF EMBRITTLEMENT OF ALUMINUM ALLOY BY LIQUID METAL[J]. 金属学报, 1998, 34(10): 1021-1027.
No Suggested Reading articles found!

Copyright © 2017 Acta Metallurgica Sinica, All Rights Reserved.
Editorial Office: Acta Metallurgica Sinica, 72 Wenhua Rd., Shenyang 110016, China
Tel: +86- 024-23971286, Fax: +86-024-23843760 　E-mail: jsxb@imr.ac.cn
Powered by Beijing Magtech